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Toxicity to microorganisms

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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1999-06-28 to 1999-07-01
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Guideline study with acceptable restrictions: Test substance not stable under test conditions
Qualifier:
according to guideline
Guideline:
EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)
Version / remarks:
Cited as Directive 87/302/EEC, part C, p. 118 (Biodegradation: Activated sludge respiration inhibition test)
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Deviations:
not specified
GLP compliance:
yes
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
METHOD OF PREPARATION OF TEST SOLUTION: 
- The test substance was added to deionized water, treated 3-4 h by ultrasound and stirred overnight before testing (equilibration phase)
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
INOCULUM/TEST ORGANISM
- Species/strain: mixed population of different microorganisms
- Sampling site: WWTP of Wupper area water authority
- Pretreatment: none
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
20 +/- 1 degree C
pH:
- pH value: 6.7 before addition of test substance; 
- 7.9-8.3 in test solutions (controls: 7.8-7.9; reference substance: 7.8-8.0) at study termination
Dissolved oxygen:
At study start:
Test media: 6.2 - 8.2 mg/L; controls: 5.9 mg/L (mean value)
At study end:
Test media: 2.7 mg/L (lowest conc.) - 8.1 mg/L (highest concentration)
Nominal and measured concentrations:
INITIAL TEST SUBSTANCE CONCENTRATION:    
100; 180; 320; 560; 1000 mg/l (nominal)
Details on test conditions:
TEST CONDITIONS
- Aeration of dilution water: permanent during preincubation
- Concentration of suspended solids: 320 mg sludge/l

ANALYTICAL PARAMETER: 
- Oxygen consumption

STATISTICAL METHODS
- Probit analysis
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
263 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Key result
Duration:
3 h
Dose descriptor:
EC10
Effect conc.:
106 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
3 h
Dose descriptor:
other: EC90
Effect conc.:
650 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Results with reference substance (positive control):
3,5-dichlorophenol: % inhibition per concentration level
2.5 mg/L: 0.7 %
5.0 mg/L: 5.5 %
10.0 mg/L: 44.7 %
20.0 mg/L: 75.2 %
40.0 mg/L: 84.0 %

Concentration: Inhibition
 100 mg/l:  17.4 %
 180 mg/l:  17.4 %
 320 mg/l:  52.1 %
 560 mg/l:  95.7 %
1000 mg/l:  96.5 %

Validity criteria fulfilled:
yes
Conclusions:
The EC50 (3 hours contact time) was determined as 236 mg/L indicating that the test substance does not pose a significant risk to bacteria
populations colonising activated sludge.
Executive summary:

The effects of isophorone diisocyanate on the inhibition of the respiration rate of activated sludge ( from a STP treating predominantly domestic sewage) was investigated by Bayer AG (2000) according to EU method C.11. The oxygen content was measured at five concentrations ranging from 100 to 1000 mg/L over a period of 3 hours. The following endpoint was derived:

EC10 (3 hours): 106 mg/L

EC50 (3 hours): 263 mg/L

The study was assessed as "reliable with restrictions".

Description of key information

The effects of isophorone diisocyanate on the inhibition of the respiration rate of activated sludge ( from a STP treating predominantly domestic sewage) was investigated by Bayer AG (2000) according to EU method C.11. The oxygen content was measured at five concentrations ranging from 100 to 1000 mg/L over a period of 3 hours.

The EC50 (3 hours contact time) was determined as 263 mg/L, the EC10 (3 hours contact time) was 106 mg/L.

Key value for chemical safety assessment

EC50 for microorganisms:
263 mg/L
EC10 or NOEC for microorganisms:
106 mg/L

Additional information